Strong players don't think in single hands — they think in ranges: the full set of hands they'd take a given action with, weighted by how often each one takes it. A range like "BTN's opening range" isn't one hand, it's a policy: 100% frequency on some hands, 50% on borderline ones, 0% on the rest.

Ranges are built out of combos — specific two-card holdings. Every pocket pair (like AA) has exactly 6 combos (choose 2 of the 4 same-rank cards). Every suited non-pair (like AKs) has 4 combos (one per suit). Every offsuit non-pair (like AKo) has 12 combos (4 × 4 minus the 4 same-suited ones) — those numbers come straight from this app's comboCount(), not a memorized rule. There are 1,326 distinct two-card combos in a 52-card deck; a range's "size" is really the combo-weighted sum across whichever of the 169 canonical hand types (pairs, suited, offsuit) it includes.

That's what the 13×13 range grid encodes. Each axis runs the 13 ranks A-through-2; the diagonal holds the 13 pocket pairs, the upper-right triangle holds suited hands, the lower-left triangle holds offsuit hands. Color intensity shows action frequency, so a glance at the grid tells you both which hands are in a range and how strongly — a hand shaded half-gold, half-grey is a mixed-frequency hand, not an all-or-nothing one.

Below is BTN's actual open-raise range from this app's preflop data — the widest of the eight raise-first-in nodes, since the button faces the fewest players left to act behind it.